Cream the butter and sugar. Mix in the egg yolk and vanilla. Mix in the flour until just combined.
Spread the cookie mixture onto a greased cookie sheet.
Bake for 20 minutes, or until golden brown. Let cool.
Peanut Butter Layer
Blend the peanut butter, powdered sugar, melted butter, and vanilla together. Once the cookie layer has cooled sufficiently, spread the peanut butter layer on top. Place in the freezer for 10 minutes.
Mocha Layer
Cream the butter. Add the sugar, cocoa powder, coffee, and vanilla extract. Spread the mocha layer on top of the peanut butter layer.